The present invention relates to a device for generating speed instruction values for an elevator.
The speed of an elevator cage is controlled by a speed instruction value. In a known elevator speed control system, a first speed instruction value which varies with time during acceleration and a second speed instruction value which decreases during deceleration are available. This will be described with reference in FIG. 1.
In FIG. 1, reference character Vp designates a speed instruction value, Vp.sub.1 a first speed instruction value during high speed running, Vp.sub.2 a first speed instruction value during low speed running (short distance running), and Vd a second speed instruction value.
During high speed running, the first speed instruction value Vp.sub.1 increases from a start point O.sub.1. When the value Vp.sub.1 increases to a point A.sub.1 corresponding to a speed instruction value v.sub.11, a switching preparation instruction is issued which results in the value Vp.sub.1 undergoing a transition from A.sub.1 to D.sub.1 to F.sub.1 with time. When the two speed instruction values become equal to each other at the point F.sub.1, the first speed instruction value is switched over to the second speed instruction value Vd. As a result, the speed instruction value Vp follows the locus O.sub.1, A.sub.1, D.sub.1, F.sub.1 and H indicated in FIG. 1, where H represents a point where the cage is to be stopped, namely, a floor from which the cage is called. The speed of the winding motor and hence the speed of the cage is controlled by the speed instruction value Vp.
When the cage while being run is called to a floor, the distance between the cage and the floor (hereinafter referred to as "a remaining distance") is calculated momentarily. For instance at the time instant B.sub.1, the remaining distance can be represented by an area B.sub.1 -A.sub.1 -F.sub.1 -H-B.sub.1. On the other hand, as the speed instruction value Vd with respect to position for the remaining distance at the time instant B.sub.1 is provided for an area E.sub.1 -C.sub.1 -F.sub.1 -H-E.sub.1 equal to the above-described area, the speed instruction value Vd is given as a speed instruction value v.sub.12 for the point C.sub.1. The area B.sub.1 -A.sub.1 -D.sub.1 -E.sub.1 -B.sub.1 is equal to the area D.sub.1 -C.sub.1 -F.sub.1 -D.sub.1. The speed instruction values Vp.sub.1 and Vd are subjected to comparison so as to detect a point A.sub.1 which corresponds to the time instant B.sub.1 when the difference v.sub.12 -v.sub.11 =Vs therebetween reaches a predetermined value, whereupon the above-described switching preparation instruction is issued.
Similar to the above-described case, during low speed running, the first speed instruction value Vp.sub.2 increases from the start point O.sub.2. When the value Vp.sub.2 reaches a point A.sub.2 indicated by a speed instruction value v.sub.21, a switching preparation instruction is issued whereupon the first speed instruction value makes a predetermined variation A.sub.2 -D.sub.2 -F.sub.2 with time. This variation (or curve) A.sub.2 -D.sub.2 -F.sub.2 has the same shape as the curve A.sub.1 -D.sub.1 -F.sub.1. Therefore, as in the above-described case, the speed instruction value Vd at the time instant E.sub.2 is given as a speed instruction value v.sub.22 for the point C.sub.2. The area B.sub.2 -A.sub.2 -D.sub.2 -E.sub.2 -B.sub.2 is equal to the area D.sub.2 -C.sub.2 -F.sub.2 -D.sub.2. A point A.sub.2 which corresponds to the time instant B.sub.2 when the difference v.sub.22 -v.sub.21 =Vs reaches a predetermined value is detected. As is apparent from FIG. 1, the area D.sub.1 -C.sub.1 -F.sub.1 is larger than the area D.sub.2 -C.sub.2 -F.sub.2. Therefore, v.sub.12 -V.sub.11 is larger than v.sub.22 -v.sub.21. That is, the difference Vs varies with speed. Accordingly, it is necessary to vary the difference Vs with speed.
However, it is difficult for a conventional floor selector to adjust the value Vs accurately. Therefore, when the speed instruction value Vp.sub.1 is switched over to the speed instruction value Vd, a shock force is imposed upon the passengers in the elevator cage.
Accordingly, an object of the present invention is to eliminate the above-described difficulty accompanying a conventional elevator. More specifically, an object of the invention is to provide a speed instruction generating device for an elevator in which the difference between the speed instruction value as a function of time and the speed instruction value as a function of position are made equal at the time of a switching preparation instruction irrespective of speed and yet with a simple construction.